A touch display screen is one of important carriers which integrates an input terminal and an output terminal. In recent years, the market demand for touch display screens is boosting alone with the emergence of series of compact light-weight handheld devices such the iPhone. Previous touch display screens each are realized by superposing a touch panel on a display screen. That is, to prepare a touch display screen, a display device and a touch panel are prepared separately and then assembled to form the touch display device, which results in a relatively high cost and a bulk display screen and does not meet the present needs for a light-weight and thin display device.
An in-cell touch display screen is less in weight but more convenient in that its display device and touch panel are formed integrally, and hence draws attentions of many people. Many researchers and developers are attempting to improve the performance of the in-cell touch display screen to satisfy actual requirements. Chinese patent application No. CN102541134A discloses a touch display device and a manufacturing method thereof, and the touch display device includes: a touch panel substrate including a touch structure layer and output lead wires of the touch structure layer, and a pixel array substrate provided with a pixel array and peripheral lead wires of the pixel array, where the output lead wires of the touch structure layer overlap the peripheral lead wires of the pixel array in a light transmittance direction. The touch display device further includes a first shielding layer disposed between drive lead wires and the peripheral lead wires of the pixel array; and a second shielding layer disposed between sense electrode lead wires and the peripheral lead wires of the pixel array. The shielding layers decrease the parasitic capacitance between the peripheral lead wires of the pixel array substrate and the output lead wires of the touch panel substrate, thus prevents the drive electrodes and the sense electrodes of the touch panel from coupling with each other through the parasitic capacitance, and hence increasing the signal-to-noise ratio.
In the prior art, although the parasitic capacitance caused by the output lead wires of the touch structure layer is decreased by shielding the output lead wires, the parasitic capacitance between the drive electrodes and the sense electrodes in the touch structure layer and the display device also significantly impacts the touch effect. Referring to FIGS. 1 and 2 in particular, FIG. 1 is a schematic view of a mutual capacitive touch display device in the prior art. And FIG. 2 is an equivalent circuit diagram of the mutual capacitive touch display device shown in FIG. 1.
The touch structure layer, which is multilayered, includes a drive electrode layer 0041, a sense electrode layer 0042, and an insulation layer disposed between the drive electrode layer 0041 and the sense electrode layer 0042. The drive electrode layer 0041, the sense electrode layer 0042 and the insulation layer are disposed to overlap each other. FIG. 2 shows structures of both the drive electrode layer 0041 and the sense electrode layer 0042.
The drive electrode layer 0041 includes a plurality of rhombic drive electrodes 00410 extending along a direction Y and connecting with each other to form drive lines, each of which is connected to an external signal 00411. The sense electrode layer 0042 includes a plurality of rhombic sense electrodes 00420 extending along a direction X and connected through metal bridges to form sense lines, each of which is connected to an external signal 00421. A gap exists between the drive electrodes 00410 and the sense electrodes 00420 to insulate the drive electrodes from the sense electrodes.
Meanwhile, in the touch liquid crystal display device of the prior art, both the drive electrodes and the sense electrodes overlap with pixel electrodes, data lines and scan lines on the array substrate, thus generating a parasitic capacitance due to such overlapping. FIG. 2 is an equivalent circuit of a traditional touch liquid crystal display device. As shown, an alternating current power supply 101 is connected to a drive line 102. The drive line 102 with a certain length is equivalent to a resistor. A mutual capacitance 103 is formed by the drive electrode and the sense electrode at their intersection, and the size of the mutual capacitance 103 changes when a touch occurs. Additionally, a parasitic capacitance 105 is formed between the drive electrode or the sense electrode and the other conducting layers.
A detecting method of the traditional mutual capacitive touch panel includes scanning each drive line 102 in sequence, i.e., applying a drive voltage 101 to each drive line 102 in sequence while the remaining drive lines are grounded, and connecting each sense line 104 on the detecting side to a detecting unit 106 to detect a signal on each sense line 105. When a finger as a conductor touches the surface of the touch panel, the mutual capacitance 103 at the touched position is changed by the capacitive sense effect of the finger. Such change can be detected by the detecting unit 106 to determine whether the touch panel is touched by the finger and where the touch occurs.
In the case a large parasitic capacitance 105, the drive signal is severely deformed. In the touch liquid crystal display device, the touch layer is close to the conductive layers such as the pixel electrodes, the data lines and the scan lines on the array substrate, causing very large parasitic capacitances that are disadvantageous for the detection of a touch signal. Furthermore, as described above, in order for light transmittance through the touch liquid crystal display device, the touch layer must employ a film made of a light-transparent material such as ITO, and the resistivity of the ITO film is significantly larger than a common metal to achieve the large resistance of the touch layer, so that the detecting sensitivity of the touch layer is reduced and the load of the touch layer is increased. Therefore, as for the touch liquid crystal display device, many problems such as decreasing the resistance and parasitic capacitance, improving light transmittance, and improving the display effect need to be solved.
Besides, if the size and the resolution of the touch panel are increased, more electrodes and lead wires are required and the above problems get more severe. Therefore, the area and resistance of the touch electrode in the in-cell touch structure need to be further optimized to meet the requirements for the in-cell touch structure. Therefore, it is essential to decrease the resistance and capacitance to solve these problems of the in-cell touch structure.